IL2 and graft versus host disease: Finally, to explore therapeutic effects on human cells, we used a xenogeneic graft-versus-host disease (xeno-GvHD) mouse model in which IL-2-expanded Tregs prevent GvHD by suppressing the proliferation of injected hPBMCs.17 Briefly, immunodeficient NSG mice were injected with a lethal dose of hPBMCs from one healthy donor and then administered 1 μg of WT-IL-2 or FSY-72 for ten consecutive days or an equal dose of PEG-WT or PEG-L72FSY every other day five times.